A common method of treating temporary or chronic pain is by application of heat to the afflicted area. Such heat treatments are used as a means of therapy for conditions which include aches, stiffness in muscles and joints, nerve pain, rheumatism and the like. These treatments include the use of whirlpools, hot towels, hydrocollators, heating pads and elastic compression bands. Many of these devices employ reusable thermal packs containing, e.g., water and microwaveable gels. In general, such devices which require the thermal source to be replenished are inconvenient to use. Further, many of these thermal units or devices do not provide long lasting heat and also do not maintain a consistent temperature over long periods of time. Depending on the length of exposure, the skin temperature needs to be maintained from about 35.degree. C. to about 55.degree. C., preferably from about 36.degree. C. to about 45.degree. C., more preferably from about 37.degree. C. to about 43.degree. C., and most preferably from about 38.degree. C. to about 42.degree. C., to achieve the desired therapeutic benefits.
The beneficial therapeutic effects from this administration of heat diminish after the heat source is removed. Therefore, depending on the temperature, it is desirable to provide a sustained heat source to the afflicted area for as long as possible, i.e., from about twenty minutes to about twelve hours, preferably from about four hours to about twelve hours, most preferably from about eight hours to about twelve hours. Disposable heat packs based on iron oxidation, such as those described in U.S. Pat. Nos. 4,366,804, 4,649,895, 5,046,479 and Re. 32,026, are known and can provide long-lasting heat. However, such devices have proven not totally satisfactory because many of these devices cannot maintain a consistent and controlled temperature and/or such thermal devices are bulky and have unsatisfactory physical dimensions which hinder their effectiveness. Specifically, such devices cannot be easily incorporated into wraps which can comfortably conform to various body contours, and hence, they deliver short duration, inconsistent, inconvenient and/or uncomfortable heat application to the body.
The present inventors have discovered that the use of thin, flexible materials and a plurality of individual heat cells spaced apart for their thermal pack improves temperature control and overcomes many of the past difficulties, but have introduced some new difficulties. Though inherently more flexible, thinner materials, when combined with a plurality of individual heat cells, can lead to difficulty retaining sufficient rigidity to maintain structural support of the heat cells in an unsupported format, prevent unacceptable stretching of structures of the thin, flexible material during processing or use, and/or ensure child resistance.
For example, thermal packs made of a 25 .mu.m thick low density polyethylene (LDPE) film, which has low rigidity, and a plurality of heat cells spaced apart, drape well around various body parts and provide comfortable heat application to the body. However, thermal packs comprising a 25 .mu.m thick LDPE film can be opened relatively easily by children, the polyethylene can stretch during processing tending to decrease process reliability, the polyethylene can stretch in use leading to deleterious product performance, and the polyethylene can cause the heat cell structure to collapse upon itself due to inadequate upward support between the heat cells when used on an incline or vertically in an unsupported format.
The present inventors have similarly discovered that the use of thin but overly rigid materials, and a plurality of individual heat cells spaced apart for their thermal pack, improves temperature control, alleviates unacceptable stretching of the material during processing or use, restores structural support of the heat cells, and restores sufficient child resistance. However, thermal packs made of the thin but overly rigid material do not drape well around various body parts, even when heated, leading to a less than optimal comfortable application of heat to the body. That is, thermal packs made of overly rigid materials conform poorly to body locations, particularly body locations which require the material to bend in three dimensions during use.
For example, thermal packs made of a 40 gram/m.sup.2 polypropylene spunbond nonwoven, which is extrusion coated with low density polyethylene or ethylene vinyl acetate copolymer (EVA) at a basis weight thickness of 50 to 75 .mu.m, is thin enough to be flexible and yet sufficiently rigid so that vertical structural support, stretching, and child resistance are not concerns, are overly rigid and conform poorly to specific body locations, even when heated; particularly those body locations which require the material to bend in three dimensions.
The present inventors have discovered that a disposable thermal pack comprising at least one continuous layer of a material which is sufficiently rigid in specific areas of the thermal packs, yet which softens in between such areas during use, preferably comprising a semirigid coextruded film of polypropylene and EVA, together with a plurality of individual heat cells, having an exothermic composition, preferably comprising a specific iron oxidation chemistry and having specific physical dimensions and fill characteristics, spaced apart and fixedly attached across the thermal pack, possess some or all of the desired properties of both the thin, overly rigid materials and the thin, flexible materials mentioned above. Active heat cells, that is, heat cells having a temperature of from about 39.degree. C. to about 60.degree. C., preferably from about 40.degree. C. to about 48.degree. C., more preferably from about 41.degree. C. to about 47.degree. C., most preferably from about 42.degree. C. to about 45.degree. C., preferably soften narrow portions of the continuous layer or layers of semirigid material which immediately surround the heat cells. All remaining portions of the continuous layer or layers which surround the softened portions remain more rigid. The narrow, softened portions act as hinges between each heat cell and the remaining, cooler, more rigid portions, bending preferentially more than either the heat cell or the more rigid portions. This results in thermal packs which possess sufficient rigidity to maintain structural support of the heat cells, to prevent unacceptable stretching of structures of the continuous layer or layers during processing or use, and to ensure child resistance, while still maintaining good overall drape characteristics when heated. The thermal packs, when incorporated into body wraps, pads, and the like, provide uniform heat coverage by having excellent conformity with various body forms.
The present inventors have also discovered that undesirable, uninterrupted fold lines across the disposable thermal pack, or select regions thereof, which comprise a semirigid coextruded film of polypropylene and EVA that does not drape well and which may only drape two dimensionally, can be minimized or eliminated altogether by selectively placing the heat cells into positions relative to each other which are sufficiently close so as to block some or all possible axes which otherwise would have passed uninterrupted between the heat cells, through the thermal pack, or select regions thereof. In addition to the placement of heat cells to minimize or eliminate undesirable, uninterrupted fold lines, active heat cells soften narrow portions of the continuous layer or layers of material which immediately surround the heat sources, while all remaining portions of the continuous layer or layers of material which immediately surround the softened portions remain more rigid. The narrow, softened portions act as hinges, between each heat cell and the remaining more rigid portions, bending preferentially more than either the heat cell or the more rigid portions. Placement of the heat cells into positions relative to each other which are sufficiently close so that the number of axes which pass uninterrupted, between the heat cells coupled with the narrow softened portions, immediately surrounding the heat cells, acting as hinges, causes the disposable thermal pack to fold along a multiplicity of short interconnected fold lines oriented in a number of different directions relative to each other. Folding along a multiplicity of interconnected fold lines results in good overall drape characteristics. When heated, as described above, the semirigid material minimizes or effectively eliminates an undesirable, two dimensional drape characteristic across the thermal pack, or select regions thereof, thereby converting the thermal pack, or select regions thereof, to possess an apparent three dimensional drape characteristic.
It is therefore an object of the present invention to provide a disposable thermal pack which comprise a unified, structure having at least one continuous layer of semirigid material which has different stiffness characteristics over a range of temperatures and a plurality of individual heat cells, which provide a controlled and sustained temperature and which reach their operating temperature range relatively quickly. The heat cells are spaced apart and fixedly attached across the unified structure of the disposable thermal pack.
It is a further object of the present invention to provide a thermal pack which can be easily incorporated into disposable body wraps, having good overall drapability while maintaining sufficient rigidity to maintain structural support of the heat cells, to prevent unacceptable stretching of the continuous layer or layers during processing or use, and/or ensure child resistance.
It is a still further object on the present invention to provide a thermal pack which adapt to a wide variety of body contours by minimizing or eliminating undesirable, two dimensional drape characteristics across the thermal pack to provide consistent, convenient and comfortable heat application.
These objectives and additional objectives will become readily apparent from the detailed description which follows.